Motor vehicles having the above features, such as those described for instance in patents U.S. Pat. No. 4,306,156 and DE-C-2,943,554, further comprise a battery of accumulators that supplies most of the time the energy consumed by their electric motor. The fuel engine of these known vehicles is only put into operation when the amount of energy available in the battery drops below a predetermined value. The fuel engine then supplies via the generator coupled thereto the energy consumed by the electric motor and that required to recharge the battery. When the amount of energy available in the battery reaches another predetermined value, greater than the preceding predetermined value, the fuel engine is stopped. The energy consumed by the electric motor is then again supplied solely by the battery. U.S. Pat. No. DE-C-2,943,554 further provides for the electric motor to be operated as a generator to brake the vehicle, the electrical energy thus produced being fed to the battery inasfar as the latter is not already fully charged.
A vehicle such as those that have just been described suffer from many drawbacks caused by the battery of accumulators with which it is provided.
Thus, for example, such a battery has a large mass, generally greater than 100 kilograms and sometimes even several hundreds of kilograms, thereby increasing the unladen mass of the vehicle provided with this battery and hence reducing the overall efficiency of the latter, i.e. the distance it can travel, all else being equal, with a given amount of energy.
Besides, such a battery has a very large volume, thereby reducing the ratio between the useful internal volume of the vehicle in which it is installed and the total volume of the latter.
Further, the cost of such a battery is high, therefor increasing the cost price of the vehicle, and its life is limited, thereby having to replace it periodically and hence increasing the maintenance costs of the vehicle.
Moreover, the large mass and large volume of such a battery give rise to serious problems as regards its installation in the vehicle, these problems being further complicated by the fact that this battery needs to be readily accessible for maintenance and/or replacement purposes, problems that can only be resolved by resorting to rather complex means whose cost still further increases the cost price of the vehicle.
It should be added that such batteries are a serious hazard for the environment in the event of an accident to the vehicle because of the large amount of polluting materials, such as lead, sulphuric acid or potassium hydroxide, they contain.